Oxidation Reduction Potential (ORP)

What is ORP?

Oxidation reduction potential (ORP), also known as REDOX, is a measurement that reflects the ability of a molecule to oxidize or reduce another molecule:

  • Oxidation is the loss of electrons, so oxidizers accept electrons from other molecules
  • Reduction is the gain of electrons, so reducers donate electrons to other molecules

Oxidation reduction potential is measured as a single voltage in millivolts (mV). Oxidizers have a positive ORP value, while reducers have a negative ORP value.

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How is ORP Measured?

ORP is measured using an electrochemical sensor called an ORP or REDOX sensor. Similar to to pH sensors, the most common type of ORP sensor is a combination sensor with a measuring electrode and a reference electrode. The measuring cell, typically a noble metal like platinum or gold, detects changes in REDOX potential, while the reference provides a stable comparison signal.

Like a pH measurement, an ORP measurement is not a direct indicator of concentration, but rather an indicator of activity. However, in solutions with one active species, like pool water containing chlorine, ORP correlates to concentration.


Our extensive line of ORP products provide options for almost any application.

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Popular ProductsSensorex ORP Best Sellers

B225 Zobell ORP Calibration Solution

Use this pre-mixed ORP calibration solution for verifying and calibrating ORP sensors. The solution standard is 228mV and is widely…

Add to Cart | $26.50

TX100 pH/ORP Loop Powered 4-20mA Transmitter

Our TX100 is a fully-featured ORP/pH transmitter for use with pH and ORP sensors. The large display shows pH/ORP value simultaneously with…

Add to Cart | $485.80

S465C-ORP – ORP (REDOX) Sensor, Extended Life Acu-Trol Direct-Fit Replacement

Our S465 series of ORP sensors deliver reliable online ORP (REDOX) monitoring as a direct-fit replacement for the Acu-Trol ORP sensor…

Add to Cart | $182.40

EM803 – Smart modules (4-20mA or MODBUS/RS485) for S8000 Series

The EM803 is our most cost-effective solution for connecting our S8000 series pH and ORP sensors to a PLC or…

Add to Cart | $314.60

ORP1000 – ORP Sensor, Polycarbonate Laboratory

The ORP1000 is a durable and easy to use ORP sensor. Great for outdoor applications, such as monitoring swimming pool…

Add to Cart | $100.60

EM802-EC – Smart Conductivity Modules (4-20mA or MODBUS/RS485) for S8000 Series

The EM802-EC is our most cost-effective solution for connecting our S8000 series Contacting Conductivity sensors to a PLC or SCADA…

Add to Cart | $314.60

TX2000 – pH & ORP Transmitter/Controller, Intelligent

Our TX2000 is an intelligent pH and ORP transmitter/controller for reading pH and ORP sensors and programmable process controls. The large…

Add to Cart | $978.50

S651CD-ORP – ORP Electrode, Submersible, Flat-Surface

This submersible ORP electrode is ideal for tanks, flumes and sewer lines. The self-cleaning, flat-surface design makes the S651CD-ORP resistant…

Add to Cart | $245.30


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